Modeling very large-fire occurrences over the continental United States from weather and climate forcing

Abstract

Very large-fires (VLFs) have widespread impacts on ecosystems, air quality, fire suppression resources, and in many regions account for a majority of total area burned. Empirical generalized linear models of the largest fires (>5000 ha) across the contiguous United States (US) were developed at ∼60 km spatial and weekly temporal resolutions using solely atmospheric predictors. Climate−fire relationships on interannual timescales were evident, with wetter conditions than normal in the previous growing season enhancing VLFs probability in rangeland systems and with concurrent long-term drought enhancing VLFs probability in forested systems. Information at sub-seasonal timescales further refined these relationships, with short-term fire weather being a significant predictor in rangelands and fire danger indices linked to dead fuel moisture being a significant predictor in forested lands. Models demonstrated agreement in capturing the observed spatial and temporal variability including the interannual variability of VLF occurrences within most ecoregions. Furthermore the model captured the observed increase in VLF occurrences across parts of the southwestern and southeastern US from 1984 to 2010 suggesting that, irrespective of changes in fuels and land management, climatic factors have become more favorable for VLF occurrence over the past three decades in some regions. Our modeling framework provides a basis for simulations of future VLF occurrences from climate projections.

Human-Related Ignitions Increase the Number of Large Wildfires across U.S. Ecoregions

“…Studies have shown that large fires are driven by antecedent climatic factors that promote fuel abundance plus extreme fire weather and climatic factors (e.g., wind, drought, high temperatures) at the time of fire ignition [3,18,26,34,49,56]. However, our results suggest that the pattern between fire size and biomass varied substantially within and across U.S. ecoregions.…”

“…Large wildfire events can be economically costly and often have pronounced negative consequences for ecosystems and societies, including losses of structures and even lives [18,49]. In recent decades, the size and number of large wildfires has increased [2,3,5], and extreme fires (termed "mega-fires") are becoming more common [11,50,51].…”

“…Given the strong correlations previously identified between large fires and climate [3,18,34,49,56], we expected large fires across the U.S. to be more likely during dry, hot summer months in the western U.S. In the eastern U.S., the seasonality of large human-caused fires was highly correlated with the seasonality of human-caused fires of all sizes across most eastern ecoregions (Figure 4).…”

“…However, when large wildfires are delineated by a fire size threshold (e.g., 100,000 acres or 40,468 ha [16]; 20,000 ha [17]; <5000 and >404 ha [18]; 404 ha [19]) the resulting large fires are located almost exclusively in the western U.S. [16]. This focus on large fires neglects a considerable amount of burned area.…”

Enhance the value of participative geospatial data, modelling using point pattern processes

“…Other authors have approached the problem of producing forest fire risk maps using methods such as GIS (Vázquez and Moreno, 1998), logistic regression (Preisler and Westerling, 2007), autologistic regression (Koutsias, 2003) and empirical generalized linear models (Barbero et al, 2014) among others. Most of such approaches are either based on pure descriptive methods or ignore the presence of spatial dependence observed in the data.…”